1. Field of the Invention
The present invention relates to a Discontinuous Reception (DRX) control method and apparatus in a wireless communication system. More particularly, the present invention relates to a DRX control method and apparatus capable of preventing system performance degradation caused by transmission mismatch between an evolved Node B (eNB), also known as a Base Station (BS), and a User Equipment (UE), also known as a Mobile Station (MS).
2. Description of the Related Art
Wireless communication systems have been developed to offer communication services to users while ensuring user mobility. Due to the rapid development of communication technologies, wireless communication systems can now provide not only voice communication services but also high-speed data communication services. Recently, standardization for a Long Term Evolution (LTE) system, one of the next-generation wireless communication systems, is underway in the 3rd Generation Partnership Project (3GPP). The LTE system, scheduled to be commercialized in 2010, implements high-speed packet-based communication at a transfer rate of a maximum of 300 Mbps.
The 3GPP LTE system uses a DRX operation as one of the techniques supported to reduce power consumption of a UE. In the LTE system, the DRX operation refers to an operation in which to reduce power consumption of a UE, the UE wakes up at a predetermined cycle to receive system information or paging messages transmitted from an eNB, and stops its reception operation for the rest of the time. The DRX operation is disclosed in the 3GPP Radio Access Network 2 (RAN2) standard TS 36.321, and it is provided that a DRX cycle is changed upon expiration of a specific timer.
The DRX operation in the 3GPP LTE system is disclosed in detail in Section 5.7 of TS 36.321. In 3GPP, the state of a UE may be divided into an idle state and a connected state according to the connection between the UE and its eNB. The idle state is a state where the connection is released, while the connected state is a state where the connection is established. When the DRX operation is set in a Radio Resource Control (RRC) connected (RRC_CONNECTED) state, the UE discontinuously monitors a Physical Downlink Control Channel (PDCCH), a control channel transmitted from the eNB, for reduction in transmission power. The discontinuous monitoring for a control channel is carried out on a predetermined-cycle basis. This cycle is called a DRX cycle. The DRX cycle is subject to change according to the DRX operation.
FIG. 1 illustrates a DRX operation in an LTE system according to the related art.
Referring to FIG. 1, a DRX cycle 101 includes an on-duration 103 in which a UE wakes up and monitors a PDCCH, or a control channel, and a DRX opportunity duration 105 in which the UE may stop the monitoring operation. The UE periodically repeats the run/stop of the monitoring operation according to the DRX cycle 101. The DRX cycle 101 refers to a cycle during which the on-duration 103 is repeated, in which a UE wakes up and monitors a PDCCH, for example, a control channel. In the LTE system, a UE may receive a PDCCH, or a control channel transmitted by an eNB, in the on-duration 103, and the UE may operate in a sleep state where it does not monitor the PDCCH during the DRX opportunity duration 105.
However, as for the DRX operation presently disclosed in the 3GPP standard, no specific method defines how a UE should operate in a subframe where the DRX cycle changes. Due to this lack of a defined method in the LTE system, the DRX cycle applied may change according to the determination time for start/non-start of an on-duration timer ‘onDurationTimer’ that counts a time of the on-duration 103.
In addition, the DRX operation presently disclosed in the 3GPP TS 36.321 standard is defined to determine whether to start the on-duration timer ‘onDurationTimer’, without taking into account the possibility that the DRX cycle may change one or more times. This may lead to inconsistency between an eNB and a UE in DRX operation and cause malfunction of the on-duration timer ‘onDurationTimer’ due to the change in DRX cycle, resulting in system performance degradation due to the transmission mismatch between the eNB and the UE.